1. Field of the Invention
The present invention relates to an electronic tide meter for calculating a high tide time and low tide time and displaying the result, a method for calculating a high/low tide time and a for executing the method.
2. Description of the Related Art
Tide, defined as the phenomenon of the rising and falling of the sea surface, is a phenomenon to which attention should be paid by those particularly engaged in fishery. Additionally, tide rise and fall are considered important also for those who enjoy shell gathering or marine sports in the coastal area.
Knowing the tide phenomenon, particularly a high tide time and low tide time within a day, is achieved by calculating tide levels based on a harmonic dissolution method. Generally, the results of tide level calculations are available to the public as regional tide information published by public agencies. High tide time and low tide time are to be known by reading the tide information.
However, such reading is inefficient for those who always require information of tide phenomenon. Also, in many cases all of the available tide phenomenon information are not always required. Thus, there has been a desire for a means to know desired tide phenomenon information, particularly high tide time and low tide time.
Under such a situation, an electronic tide meter has been proposed which derives a tide level estimating equation from previously stored tide data and calculates a desirably-dated high tide time and low tide time using the derived tide level estimating equation to calculated and display the result. The tide level estimating equation is a calculating equation prescribed by the harmonic dissolving method using empirically-obtained regional tide data, to determine a tide level at a certain time. For example, according to an electronic tide meter disclosed in JP-B-6-27868 publication, tide levels at a certain time interval corresponding to one day are determined using the above-described tide level estimating equation, and from the determined tide data a extreme values are derived by a approximation method. Then, from the derived extreme values an extreme value with only a proper time interval obtained. The extreme value as a high tide or low tide level is calculated for a high tide time and low tide time.
Meanwhile, according to a tide display apparatus disclosed in JP-A-58-146819 publication, a tide as determined from the above-described tide level estimating equation is graphically displayed to enable reading a high tide time and low tide time from a displayed graph.
However, in order to determine a high tide time and low tide time with accuracy, it is required in the above-mentioned tide level estimating equation to determine the increased number of tide levels with a time interval that is as short as possible. To achieve this, memory with a large capacity had to be used to store many calculated tide data further there is an increased operation time.
In the electronic tide meter disclosed in the above-mentioned JP-B-6-27868 publication, in order to determine a high tide time and low tide time with higher accuracy, it has also been required to determine much of tide data from the tide level estimating equation using a short time interval.
Further, the above-mentioned tide display apparatus disclosed in the JP-A-58-146819 publication time and low tide time, and includes a similar problem to the electronic tide meter disclosed in the JP-B-6-27868 publication.